Reliability Evaluation Of Multi-Infeed HVDC System

With the implementation of the strategy "power transmitting from west to east" and the development of nation-wide interconnection, several EHVDC transmission systems over long distance and carrying bulk capacity are built up and put into service recently. A novel configuration of HVDC transmission systems - Multi-infeed HVDC system has appeared in China Southern Power Grid. As a complicated system, it is insistent and necessary to evaluate its reliability.Multi-infeed HVDC system features a mass of elements, various states and the complexity of the calculation conditions, which lead to the difficulty of its reliability evaluation. The focus of the reliability evaluation for such system is how to establish a simple and easily solved mathematical model that also meets the engineering requirements. In this paper, based on the idea of recurrence equivalent model, the theory of connectivity and the concept of minimum cut set, the reliability equivalent model of HVAC system is established. And the reliability equivalent model of HVDC system is also achieved employing the principle of Analytics Method. Thus, the reliability equivalent model for Multi-infeed HVDC system is built up on the practical circuit base.The basic methods applied in power system reliability evaluation are FD Analytics Method and Monte Carlo Simulation Method. After analyzing the merits and demerits of FD Analytics Method and Monte Carlo Simulation Method respectively, a comprehensive method combining the above two basic methods is presented and employed in the reliability evaluation of Multi-infeed HVDC system. Its main point is: FD Analytics Method is employed to construct the reliability equivalent model of HVDC transmission system and the substations. Monte Carlo Method is used for simulating the transfer of the element states. Analytics Method is also performed to determine the mean duration of any simulated system states. So the efficiency and accuracy of simulation are improved considerably with this comprehensive method.In order to make the comprehensive method more useful when it is employed to assess the reliability of the practical Multi-infeed HVDC system, an improvement is made to this method. According to the computational diagram which has been improved, the whole evaluating process is divided into two parts, one is using Monte Carlo method to randomly simulate the state of each element and the other is calculating the load shed of the various faults based on the theory of LSC, which is to form the matrix for state analysis and calculate the reliability indicators of the system. Thus the system reliability evaluating results are achieved. It turns out that the improved method is more suitable to the practical Multi-infeed HVDC system.A reliability evaluation of a particular 500kV Multi-infeed HVDC system is carried out according to the basic principle of the improved and comprehensive method. After synthetically analyzing the reliability results and through the weakness calculation, a series of enhancing measures are proposed. It is proved that this method is correct and efficient.